The present invention relates to a cleaning unit employed in electrophotographic copiers, printers, and the like, an image forming method and an image forming apparatus employing said cleaning unit.
In recent years, organic photoreceptors (hereinafter referred simply to as photoreceptors), comprising organic photoconductive materials, have been most widely employed as the image bearing body employed in electrophotographic image forming apparatuses. Compared to other photoreceptors, organic photoreceptors exhibit advantages in such a manner that it is easy to develop materials which correspond to various types of exposure light sources ranging from visible light to infrared rays; it is possible to select materials which result in minimum environmental pollution; their production cost is lower, and the like. However, said organic photoreceptors exhibit disadvantages in that the mechanical strength is insufficient, and during producing numerous copies and prints, the photoreceptor surface tends to be degraded or abraded.
Further, said organic photoreceptor exhibits large contact energy with the toner, which visualizes the electrostatic latent images formed on the photoreceptor. As a result, it is difficult to remove the resulting residual toner, which remains on the photoreceptor after transferring said toner image onto a transfer material in the transfer process. Thus various problems regarding the cleaning on the photoreceptor surface tend to occur.
On the other hand, due to the progress of digital technology in recent years, an image forming method utilizing a digital system has played an increasing role in the image forming method utilizing the electrophotographic system. The image forming method utilizing said digital system is basically carried out in such a manner that an image comprised of small dots, called pixels, of 400 dpi, and the like, is visualized. Demanded thus is a high image quality technique which faithfully reproduces images comprised of such small dots.
In order to realize such desired high image quality technique, one of the most important techniques is one which relates to toner production. Heretofore, for forming electrophotographic images, mainly employed has been a so-called pulverized toner which is prepared in such a manner that toner powder, which is obtained by blending and kneading binder resins with pigments and then pulverizing the resultant mixture, is subjected to classification during a classifying process. However, the toner obtained through such production processes exhibits limitation in making the particle size distribution of toner particles uniform. As a result, the particle size distribution, as well as the shape of toner particles, has not been sufficiently uniform. Thus in electrophotographic images obtained by employing such pulverized toner, it is difficult to achieve the desired high image quality.
In recent years, as a means to achieve uniform size distribution as well as uniform shape of said toner particles, proposed have been electrophotographic developer materials or image forming methods utilizing polymerized toner. Said polymerized toner is produced by uniformly dispersing monomers as the raw material in water based system and then polymerizing the resultant dispersion. As a result, it is possible to obtain a toner having a uniform size distribution as well as uniform shape.
Herein, when said polymerized toner is applied to an image forming apparatus utilizing an photoreceptor, new technical problems have surfaced. Namely, as described above, the toner particle shape of said polymerized toner is formed during the monomer polymerization process. As a result, said shape is formed to be nearly spherical. As is already well known, toner of a spherical shape, which remains on said organic photoreceptor, tends to be insufficiently removed. Specifically, the surface of the organic photoreceptor tends to be worn. When toner particles adhere to the roughened surface, caused by said wear, fine toner particles are not completely removed by cleaning, in such a range that the resultant images are not visually affected. Such toner particles, which have not been removed, stain charging members (such as charging wires and charging rollers). As a result, halftone images, and the like, are subjected to formation of image unevenness.
In order to minimize blade curl, which is generated by the image forming method employing the polymerized toner as described above, as well as to insufficient cleaning such as residual toner which has not been removed, heretofore, various proposals have been made. Of these, applied has been one proposal in which the shape of the polymerized toner is varied from a circular shape to an elliptic shape, and another in which the surface shape of the polymerization toner surface is varied into the irregular one. However, these proposals have not sufficiently overcome the stated problems.
An object of the present invention is to provide a cleaning unit which overcomes the aforementioned problems, and upon using an organic photoreceptor and a polymerized toner, maintains the desired cleaning performance for an extended period of time, results in no image problems and is capable of forming excellent electrophotographic images, and an image forming method and an image forming apparatus using said cleaning unit.
In order to overcome the aforementioned problems, the inventors of the present invention have made investigations. As a result, by adhering a second blade member onto a first blade member, it has become possible to secure excellent cleaning properties, and to maintain stable vibration of said first blade member. Thus it has become possible to overcome the aforementioned problems. Namely, it has been discovered that the object of the present invention is achieved by employing any of constitutions described below.
1. In a cleaning unit having a first blade member which removes residual toner on an organic photoreceptor after developing an electrostatic latent image formed on said organic photoreceptor, employing a developer comprising a toner and subsequently transferring a toner image, visualized through said development, onto a transfer material from said organic photoreceptor, a cleaning unit wherein said cleaning unit comprises a cleaning blade composed of a cleaning blade composed of a first blade member and a second blade member; said first blade member is brought into close contact with said second blade member on the side opposite to that which is brought into contact with said photoreceptor; and a level difference is provided between the edge of said first blade member and the edge of the said second blade member in such a manner that said level difference is positioned so that said second blade member is more apart from said organic photoreceptor.
2. In a cleaning unit having a first blade member which removes residual toner on an organic photoreceptor after developing an electrostatic latent image formed on said organic photoreceptor, employing a developer comprising a toner and subsequently transferring a toner image, visualized through said development, onto a transfer material from said organic photoreceptor, a cleaning unit wherein said cleaning unit comprises a cleaning blade composed of a cleaning blade composed of a first blade member and a second blade member; said first blade member is brought into close contact with said second blade member on the side opposite to that which is brought into contact with said photoreceptor; and the free length xe2x80x9caxe2x80x9d of said blade and the free length xe2x80x9cbxe2x80x9d of said second blade member satisfy Formula 1.
0.1 less than b/axe2x89xa60.9xe2x80x83xe2x80x83Formula 1
3. In a cleaning unit having a first blade member which removes residual toner on an organic photoreceptor after developing an electrostatic latent image formed on said organic photoreceptor, employing a developer comprising a toner and subsequently transferring a toner image, visualized through said development, onto a transfer material from said organic photoreceptor, a cleaning unit wherein said cleaning unit comprises a cleaning blade composed of a first blade member and a second blade member; said first blade member is brought into close contact with said second blade member on the side opposite to that which is brought into contact with said photoreceptor; and thickness t1 of said first blade member and thickness t2 of said second blade member satisfy Formula 2.
xe2x80x831/30 less than t2/t1 less than 2xe2x80x83xe2x80x83Formula 2
4. In a cleaning unit having a first blade member which removes residual toner on an organic photoreceptor after developing an electrostatic latent image formed on said organic photoreceptor, employing a developer comprising a toner and subsequently transferring a toner image, visualized through said development, onto a transfer material from said organic photoreceptor, a cleaning unit wherein said cleaning unit comprises a cleaning blade composed of a first blade member and a second blade member; said first blade member is brought into close contact with said second blade member on the side opposite to that which is brought into contact with said photoreceptor; and hardness K1 of said first blade member specified by JIS A xe2x80x9cHardnessxe2x80x9d, and thickness K2 of said second blade member, specified in the same, satisfy Formula 3.
5/7 less than K2/K1 less than 10/7xe2x80x83xe2x80x83Formula 3
5. In a cleaning unit having a first blade member which removes residual toner on an organic photoreceptor after developing an electrostatic latent image formed on said organic photoreceptor, employing a developer comprising a toner and subsequently transferring a toner image, visualized through said development, onto a transfer material from said organic photoreceptor, a cleaning unit wherein said cleaning unit comprises a cleaning blade composed of a first blade member and a second blade member; said first blade member is brought into close contact with said second blade member on the side opposite to that which is brought into contact with said photoreceptor; and impact resilience H1 of said first blade member and impact resilience H2 of said second blade member satisfy Formula 4.
2/7 less than H2/H1xe2x89xa68/7xe2x80x83xe2x80x83Formula 4
6. In a cleaning unit having a first blade member which removes residual toner on an organic photoreceptor after developing an electrostatic latent image formed on said organic photoreceptor, employing a developer comprising a toner and subsequently transferring a toner image, visualized through said development, onto a transfer material from said organic photoreceptor, a cleaning unit wherein said cleaning unit comprises a cleaning blade composed of a first blade member and a second blade member; said first blade member is brought into close contact with said second blade member on the side opposite to the side which is brought into contact with said photoreceptor; a level difference is provided between the edge of said first blade member and the edge of the said second blade member in such a manner that said level difference is positioned so that said second blade member is more apart from said photoreceptor; and said first blade member and said second blade member satisfy Formulas 1 through 4.
7. An image forming method wherein after developing an electrostatic latent image formed on a photoreceptor, employing a developer comprising a toner and subsequently transferring a toner image, visualized through said development, onto a transfer material from said photoreceptor, any residual toner on said photoreceptor is removed employing a cleaning unit described in any one of 1. through 5. above.
8. An image forming apparatus wherein after developing an electrostatic latent image formed on a photoreceptor, employing a developer comprising a toner and subsequently transferring a toner image, visualized through said development, onto a transfer material from said photoreceptor, residual toner on said photoreceptor is removed employing said cleaning unit.
9. Preferably employed as said toner is one in which the variation coefficient of the shape coefficient of toner particles is not more than 16 percent, and the number variation coefficient of the number size distribution of said toner particles is not more than 27 percent.
10. Preferably employed as said toner is one which comprises at least 65 percent by number of toner particles in the range of the shape coefficient of 1.2 to 1.6.
11. Preferably employed as said toner is a toner which comprises at least 50 percent by number of toner particles having no corners.
12. Said photoreceptor preferably comprises an electrically conductive support having thereon a photosensitive layer, which preferably comprises, in the surface layer, polycarbonate having an average molecular weight of at least 40,000.